There are numerous types of valves for controlling fluid flow along a fluid pathway, such as, check valves, plug valves, ball valves, stop or globe valves, angle valves, butterfly valves, and gate valves. Many valves, for example, ball valves, globe valves, butterfly valves, and gate valves, include a valve stem that control motion of a valve element. For example, the valve stem may communicate motion from an exterior portion of the valve (e.g., actuator, handle, crank, wheel, etc.) to an interior portion of the valve (e.g., the valve element, such as, a ball, plate, gate, disc, plug, etc.).
In valves that include a valve stem, a seal is generally created between the valve body and the valve stem in order to prevent or minimize fluid from traveling outside of a fluid flow portion of the valve body. In some valves the seal is created with packing material. For example, U.S. Pat. No. 4,256,317, the disclosure of which is incorporated herein in its entirety by this reference, teaches a valve packing system including compacted graphite material. Such graphite material may be formed from spirally coiled graphite tape as disclosed in U.S. Pat. No. 4,394,023, the disclosure of which is incorporated herein in its entirety by this reference.
The packing material is generally contained in a packing stack. The packing stack may include packing caps (e.g., end rings, guide rings, etc.) on outer ends of the packing stack configured to retain the packing material in position. For example, packing caps are taught by U.S. Pat. Nos. 4,256,317 and 6,116,573, the disclosure of each of which is incorporated herein in its entirety by this reference. The packing caps may be used to transmit compressive forces on the packing material to maintain a seal against the valve stem.